CN102652181B

CN102652181B - Steel sheet with small welding deformation and excellent corrosion resistance

Info

Publication number: CN102652181B
Application number: CN201180004583.XA
Authority: CN
Inventors: 上村隆之; 鹿岛和幸; 幸英昭; 川畑友弥; 中村浩史; 有持和茂
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2010-01-18
Filing date: 2011-01-17
Publication date: 2014-06-25
Anticipated expiration: 2031-01-17
Also published as: WO2011087116A1; JP4924775B2; JPWO2011087116A1; CN102652181A; KR20110105400A

Abstract

Disclosed is a steel sheet with small welding deformation and excellent corrosion resistance, which is characterized by having a chemical composition containing, in mass%, 0.02-0.25% of C, 0.01-0.7% of Si, 0.3-2% of Mn, 0.05% or less of P, 0.008% or less of S, less than 0.2% of Cu, 1-2.5% of Cr, 0.05% or less of Mo, 0.005-0.1% of Nb, 0.003-0.1% of Al, 0.01% or less of N and 0.03-0.50% of Sn, with the balance made up of Fe and impurities and a Cu/Sn ratio of 1 or less. The steel sheet is also characterized in that the metallic structure thereof is composed of 10-60% of a ferrite structure and 40-90% of a bainite structure and/or a martensite structure, the ferrite structure has an average particle diameter of 30 [mu]m or less, and the ratio of the hardness of the bainite structure and/or the martensite structure to the hardness of the ferrite structure is 1.5 or more. The steel sheet may additionally contain one or more substances selected from among Ti, Ni, V, B, Zr, Ca, Mg and REM.

Description

The steel plate of the less and excellent corrosion resistance of welding distortion

Technical field

The present invention relates to a kind of that in the fields such as shipbuilding, oceanic tectonic thing, building construction, bridge, building, adopt, welding distortion is less and the steel plate of excellent corrosion resistance.Particularly relate to the steel plate of the less and excellent corrosion resistance of a kind of welding distortion producing in the time of fillet weld seam operation.

Background technology

Conventionally,, in the time making various weldable steel structure, the contraction, the expansion that are caused by the solidification shrinkage of welding metal and cooling and phase transformation afterwards thereof cause deforming.As the representative of welding distortion, can list the angular distortion of T-shaped fillet weld seam portion.While making structure in residual angle of entry shifting ground, significantly reduction or destruction characteristic are deteriorated due to the distortion of member for buckling strength, therefore, likely do not become the structure that planner expects.In order to prevent this state of affairs, seek to prevent countermeasure by carrying out various research.

The welding distortion of application is at present prevented to countermeasure rough classification, have following (i)～(iii) these 3.

(i) the research (raising is deformed the method for the rigidity of member) of design

The residual reason of welding distortion is because be subject to viscous deformation near the solder terminal portion of welding metal, mother metal.The position that has been subject to viscous deformation makes its Outboard Sections recoverable deformation, but higher in rigidity, sectional area is larger in the situation that, the deflection that has been subject to the position of viscous deformation diminishes.Thereby increasing section long-pending ground design alteration can prevent countermeasure as one.But, rise at the cost that uses steel, weight rises and aspect the duration is long-term, the loss of the long-pending such design alteration of increasing section is more.

(ii) the research while welding

In the time of welding, can study to prevent welding distortion by carrying out certain.There is several method, but first bending to opposite direction in advance before welding.Though produce angular distortion after welding, likely by being finish-machined to target shape to bending in the other direction in advance.In addition, also exist when welding to retrain end and the method for allowable strain not.And, sometimes also adopt the method that suitable position is reheated reverse Hui Zhi by rear row welding torch is set after welding.But, owing to being all accompanied by increasing considerably of workload, therefore, become the major cause that cost rises.

(iii) the processing of the rectification after welding

As the method for correcting after welding, exist mechanical checkout and wire to add hot straightening.But these methods also need to increase considerably workload, and, skilled prowess also required.

(i) above-mentioned～countermeasure is (iii) all the research on making, but for example in patent documentation 1, has proposed to seek to reduce welding distortion by the research of welding material.But, rising infringement economy or effect when insufficient at the cost of welding material, more problems, is the situation that cannot apply in reality.

With respect to this, also there is the example of wanting to suppress by the research of the steel as mother metal welding distortion, several schemes have been proposed as described as follows.

In patent documentation 2, disclose and a kind ofly promoted separating out in welding heat course to improve the method for yielding stress by compound interpolation Nb and Mo.But particularly the interpolation of Mo can cause significantly cost to rise, and therefore lacks versatility.

In patent documentation 3 and patent documentation 4, record following content: by bainite and/or martensitic point of rate as the steel of mother metal are controlled at more than 20%, and stipulate the dispersion state of carbonitride, improve yielding stress, suppress thus welding distortion.But, might not reach in practical and obtain sufficient welding distortion reduction effect.

And, in patent documentation 5, record following content: be more than 70% by making as the bainite rate of the steel of mother metal, and guarantee that solid solution Nb amount is more than 0.040%, to suppress welding distortion.But, be 70% when above in bainite point rate, the intensity that not only can produce mother metal departs from the situation of general context, and the infringement of the welding crack being caused by Nb also likely becomes problem.

On the other hand, weldable steel structure mostly by the sea area, be scattered with under the more environment of the salt amount of wafting such as area of snow melt salt, and in shipbuilding field, under seawater spittle environment, use.

Conventionally, when weather resistant steel is exposed in atomospheric corrosion environment, be formed with the rusty scale with protectiveness on its surface, the Corrosion Of Steel after suppressing.Therefore, weather resistant steel can safeguard that steel are used for the structures such as bridge by the minimum of open ground use as not application.

But; not only area by the sea, even in inland portion, waft in the more area of salt amount like that in the area that is furnished with snow melt salt, frostproofer at astigmatism; also be difficult to be formed with the rusty scale with protectiveness on the surface of weather resistant steel, be difficult to the effect that performance suppresses corrosion.Therefore, in these areas, cannot use exposed weather resistant steel, application is used the ordinary steel that ordinary steel is implemented application and used conventionally.But, in the situation that application is used this ordinary steel, cause film deteriorated by corrosion, needs application again in approximately every 10 years, therefore, the expense that maintains administrative institute's need is very large.

In recent years, reach 0.05mg/dm in the salt amount of wafting in NaCl ²/ day(0.05mdd) above area, for example, in riviera, utilize the standardized climate-resistant steel of Japanese Industrial Standards (JIS) (JIS G 3114: welding structure weathering resistance hot-strip) because producing squamous rust, stratiform rust etc. and the amount of being corroded is larger, therefore, cannot without application in the situation that, use (with reference to building province building institute, (company) steel social hall, (company) Japanese bridge is built association: be applied to the design and construction main points that the joint research report (XX) that bridge is relevant-nothing is coated with weathering resistance bridge (change edition-1993.3) to climate-resistant steel).

Like this, wait under the more environment of salinity in area by the sea, conventionally common iron is carried out to application and process.But present situation is: build near riviera river mouth, sprinkled with the bridge corrosion in the road of the intermountain portion of snow melt salt etc. significantly, no longer application.For these again application to spend great workload, therefore, strong request can without application the steel that use.

Recently, having developed the Ni that the Ni of a kind of interpolation 1%～3% left and right forms is high weather resistance steel.But, can clearly be greater than in the area of 0.3mdd～0.4mdd in the salt amount of wafting, in the situation that only adding this Ni, be difficult to be applied to can without application the steel that use.

Because the corrosion of steel becomes along with the salt amount of wafting increases acutely, therefore, from the viewpoint of erosion resistance and economy, need the waft weather resistant steel of salt amount of quartz.In addition, even bridge, according to the place using, the difference at position, the corrosive environment of steel is also different.For example, in crossbeam outer exposed in rainfall, dew with in sunshine.On the other hand, though be exposed in dew in crossbeam inside, can not be caught in the rain.Conventionally,, in the more environment of the salt amount of wafting, can say that the corrosion of crossbeam inside is outside more violent than crossbeam.

In addition, in the environment sprinkled with snow melt salt, frostproofer on road, the car during this salt is traveling is rolled, and is attached on the bridge of supporting road, therefore, becomes harsh corrosive environment.And away from inferior being also exposed under harsh salt damage environment of eaves of seashore, in this area, becoming the salt amount of wafting is harsh corrosive environment more than 1mdd slightly.

In order to tackle this problem, the steel of the corrosion under the more environment of a kind of salt amount that prevents from wafting had been developed in the past.

For example, the weather resistant steel that a kind of increase chromium (Cr) amount forms is proposed in patent documentation 6, and, the weather resistant steel that a kind of increase nickel (Ni) amount forms has been proposed in patent documentation 7.

But, the increase chromium (Cr) that above-mentioned patent documentation 6 proposes, although can improve weathering resistance in the region of the salt amount of wafting of the weather resistant steel that amount forms below to a certain degree, makes on the contrary weathering resistance deteriorated under the harsh salt time-sharing environment that exceedes this degree.

In addition, the weather resistant steel that increase nickel (Ni) amount proposing at above-mentioned patent documentation 7 forms, though weathering resistance improves to a certain extent, the cost of steel self raises, very expensive as the material for purposes such as bridges.For fear of this point, in the time reducing Ni amount, how weathering resistance is not improved, in the situation that the salt amount of wafting is more, be created in steel surface generate stratiform peel off rust, corrode remarkable, be unable to undergo the such problem of life-time service.

Patent documentation 1: Japanese kokai publication hei 7-9191 communique

Patent documentation 2: Japanese kokai publication hei 7-138715 communique

Patent documentation 3: TOHKEMY 2003-268484 communique

Patent documentation 4: TOHKEMY 2006-2211 communique

Patent documentation 5: TOHKEMY 2006-2198 communique

Patent documentation 6: Japanese kokai publication hei 9-176790 communique

Patent documentation 7: Japanese kokai publication hei 5-118011 communique

Like this, in previous methods, from the viewpoint of having difficulties respectively of economy and reproducibility, the leeway of improvement is very large in practical.

Particularly, in the welding structure thing that the Plate Steel more than used thickness 15mm is manufactured, even if the deflection of each weld is less, welding structure thing entirety also can produce larger distortion, therefore, need to do one's utmost to reduce welding deformation amount.In addition, the upper limit of thickness is not particularly limited, but preferably can process the Plate Steel that reaches 50mm.

And in the weldable steel structure using under the more environment of the salt amount of wafting, the separability of resistance to application becomes very large problem.; as noted above, in the environment that has coastal environment that a large amount of muriates wafts, be scattered with Snow Agent or frostproofer, even if implement application; also exist application to peel off very soon and corrode such problem, needing every several years～more than ten years to implement the brushing again of application.In addition, in the time implementing the brushing again of application, as its front operation, need on bridge once, assemble scaffolding and again implement sandblasting having corroded, therefore will spend great cost.And even be also difficult to completely except derust in the situation that again implementing sandblasting, even cannot be completely except application again on the steel that derust, the application life-span also significantly shortens.In the most situation of the separability of resistance to application, depend on that the corrosion resistance of steel comprising as substrate is in interior characteristic.

Thereby strong expectation extends the life-span of application and will study for a second time courses one has flunked overlay painting interval and draw longlyer.That is, needing in the ship domain of application, bridge field, the requirement of product life minimization of cost is also higher, and on the basis of product-life-management of considering bridge, it is also very important extending the application life-span.

Summary of the invention

the problem that invention will solve

The present invention In view of the foregoing, establishes with low cost and suppresses reliably the technology of welding distortion, and the steel plate that provides a kind of welding distortion less is provided its object, particularly, object be to provide a kind of in fillet weld seam the less steel plate of welding distortion.In addition, the target value of welding deformation amount be in the past steel 1/2.

The present invention also aims to provide also very good steel of erosion resistance in a kind of perchloride environment (comprise that application is unstripped and suppress the corrosion of painting defect portion and maintain erosion resistance (separability of resistance to application) and weathering resistance during without application).

for the scheme of dealing with problems

The inventor etc., in order to solve this problem, based on the result of various researchs, stipulate the chemical constitution of steel plate, and, also its metallographic structure is stipulated.Fig. 1 represents to utilize the Thermal-mechanical Coupling FEM simultaneously implementing with experiment to resolve the independently impact of the each material property value obtaining.In addition, Fig. 2 represents the design conditions that FEM resolves.

In Fig. 1, transverse axis is thermal conductivity (line of the white circle of mark), transformation temperature Ac ₁(marking the line of black circle), intensity TS(mark tetragonal line), the longitudinal axis represents angular distortion amount.As shown in Figure 1, even if increase the thermal conductivity of steel plate, angular distortion amount also can not change, and in the time that transformation temperature rises, angular distortion quantitative change is large, and in the time that intensity becomes large, angular distortion quantitative change is little.Therefore, welding distortion particularly depends on intensity, transformation temperature largely, is steel (angular distortion amount is about 0.8mm) in the past 1/2, when 0.4mm in the target value that makes welding deformation amount (angular distortion amount), and intensity is high, departs from general intensity rank.Depart from general intensity rank and be not only outside the object in common business transaction, also likely produce the problem in structure design, the problem of weldability simultaneously, unsatisfactory.

Therefore, inventor's etc. target is to develop a kind of steel grade that is keeping the normal temperature strength of applicable general intensity rank just can increase hot strength.

In addition, it is said in the past the resultful Mo of the increase of hot strength was caused to cost of alloy costliness, caused that cost rose, therefore also unrealistic.Therefore, the inventor etc. are conceived to less expensive and also less to the detrimentally affect of weldability Cr, have implemented various tests.As a result, obtained the opinion shown in following (a)～(d).

(a) Cr can increase hot strength.Containing Cr 1.0% when above, even if do not make Mo coexist, also can guarantee hot strength, can suppress fully thus welding distortion.But, in the time that the amount of Cr is less than 1.0%, in the situation that Mo is not coexisted, can not guarantee fully hot strength.

(b) in addition, must contain Nb.By containing Nb, can guarantee fully hot strength.In addition, the addition of Nb, for better on a small quantity, is more than 0.00 5%.

(c) in order to be suitable for general intensity rank, must contain ferritic structure.From the viewpoint of toughness, the crystal grain diameter of ferritic structure need to be below 30 μ m.In addition, for welding distortion is minimized, the harder mode of the hardness of the hard phase being made up of bainite structure or martensitic stucture is good, need to be more than 1.5 firmly with the hardness ratio of soft phase.

(d) manufacture method of steel plate can be also common condition, but has the tendency that hardening capacity is higher compared with common steel, therefore, preferably studies in order to be suitable for general intensity rank.

On the other hand, the result based on the corrosion under the more environment of the salt amount of wafting is studied such as the inventor, finds under such environment FeCl ₃the dry wet of solution is the essential condition of corrosion repeatedly, utilizing Fe ³⁺hydrolysis make, under state that pH reduces, and to pass through Fe ³⁺the effect of playing oxygenant is accelerated corrosion.

Corrosion reaction is now as described below.

As cathodic reaction, reaction below main generation.

Fe ³⁺+ e ^-→ Fe ²⁺(Fe ³⁺reduction reaction)

And, except this reaction, also there is following cathodic reaction simultaneously.

2H ₂O＋O ₂＋2e ^－→4OH ^－

2H ^＋＋2e ^－→H ₂

On the other hand, with respect to above-mentioned Fe ³⁺reduction reaction, there is following anodic reaction.

Anodic reaction: Fe → Fe ²⁺+ 2e ^-(solubilizing reaction of Fe)

Thereby the combined reaction of corrosion is as following (1) formula.

2Fe ³⁺+ Fe → 3Fe ²⁺(1) formula

The Fe that utilizes the reaction of above-mentioned (1) formula to generate ²⁺be oxidized to Fe by atmospheric oxidation ³⁺, the Fe of generation ³⁺again play the effect of oxygenant, accelerated corrosion.Now, Fe ²⁺the speed of response of atmospheric oxidation conventionally slower under low pH environment, but accelerate in dense thick chloride soln, be easy to generate Fe ³⁺.Owing to being the reaction of such circulation, therefore, can be clearly under the very many environment of the salt amount of wafting, sustainable supply Fe all the time ³⁺, the corrosion of steel is accelerated, and erosion resistance is significantly deteriorated.

The mechanism of corrosion based on in this salt time-sharing environment such as the inventor, studies the impact of weathering resistance various alloying elements, and result has drawn the opinion shown in following (e)～(g).

(e) Sn is as Sn ²⁺dissolve, utilize 2Fe ³⁺+ Sn ²⁺→ 2Fe ²⁺+ Sn ⁴ ⁺reaction make Fe ³⁺concentration reduce, thereby suppress the reaction of (1) formula.Sn also has the such effect of the anode dissolution of inhibition.

(f) Cu was the basic element that improves effect in the more environment of the salt amount of wafting as erosion resistance in the past, manifests erosion resistance and improve effect in long environment of moistening time.But, the environment of can be clearly larger at chloride concentration, the local decline of pH, for example by salinity adhere to, humidity changes do and wetly repeatedly generates under the so more dry environment of β-FeOOH, Cu on the contrary promotes to corrode.

(g) steel that like this, contain energetically Sn and suppressed Cu amount can be expected higher erosion resistance.And because erosion resistance is higher, therefore, even steel are carried out to application, the application being caused by Corrosion Of Steel is peeled off also less, suppress the corrosion of painting defect portion.On the other hand, also can expect the anticorrosion ability of film, therefore, the in the situation that of application, can expect the effect of higher erosion resistance.Thereby, except erosion resistance, also there is the life-span that can extend application, by the effect of studying for a second time courses one has flunked overlay painting interval and drawing longlyer.Particularly in the improvement of the separability of resistance to application in ship domain, bridge field, bring into play effect.

The present invention completes as basis take above-mentioned opinion, and its purport is the steel plate of the less and excellent corrosion resistance of the welding distortion shown in following (1)～(4).

(1) steel plate of the less and excellent corrosion resistance of a kind of welding distortion, it is characterized in that, there is such chemical constitution, , in quality %, contain C:0.02%～0.25%, Si:0.01%～0.7%, Mn:0.3%～2%, below P:0.05%, below S:0.008%, Cu: be less than 0.2%, Cr:1%～2.5%, below Mo:0.05%, Nb:0.005%～0.1%, Al:0.003%～0.1%, following and Sn:0.03%～0.50% of N:0.01%, remainder is made up of Fe and impurity, and Cu/Sn ratio is below 1, metallographic structure is made up of 10%～60% ferritic structure and 40%～90% bainite structure and/or martensitic stucture, and, the median size of this ferritic structure is below 30 μ m, the hardness of bainite structure and/or martensitic stucture is more than 1.5 with the ratio of the hardness of ferritic structure.

(2) according to the steel plate of the less excellent corrosion resistance of the welding distortion of above-mentioned (1), it is characterized in that, in quality %, this steel plate also contains below Ti:0.1%.

(3) according to the steel plate of the less excellent corrosion resistance of the welding distortion of above-mentioned (1) or (2), it is characterized in that, in quality %, this steel plate also contain that Ni:3.5% is following, V:0.1% following, B:0.004% is following and Zr:0.02% with lower one or more.

(4) according to the steel plate of the less excellent corrosion resistance of the welding distortion of any one in above-mentioned (1)～(3), it is characterized in that, in quality %, this steel plate also contain that Ca:0.004% is following, Mg:0.002% following and REM:0.002% with lower a kind of or two or more.

In addition, time of the present invention from the viewpoint of investigating of the less welding process of the welding distortion of steel plate, think: the welding distortion of steel plate is in fact the welding distortion of welding heat affected zone, therefore, in welding heat affected zone, as long as weld meeting on the basis of prescribed condition, just can improve welding distortion inhibition energy.

Thereby, from the viewpoint of welding process, the present invention also can hold as " a kind of welding process of steel plate, this steel plate has such chemical constitution, , in quality %, contain C:0.02%～0.25%, Si:0.01%～0.7%, Mn:0.3%～2%, below P:0.05%, below S:0.008%, Cu: be less than 0.2%, Cr:1%～2.5%, below Mo:0.05%, Nb:0.005%～0.1%, Al:0.003%～0.1%, following and Sn:0.03%～0.50% of N:0.01%, remainder is made up of Fe and impurity, and Cu/Sn ratio is below 1, it is characterized in that, the metallographic structure by the position that becomes welding heat affected zone of welding front spring is made up of 10%～60% ferritic structure and 40%～90% bainite structure and/or martensitic stucture, and, the median size of this ferritic structure is below 30 μ m, the hardness of bainite structure and/or martensitic stucture is more than 1.5 with the ratio of the hardness of ferritic structure.”。

Certainly, this steel plate also can be in quality %, also contain that Ti:0.1% is following, Ni:3.5% following, V:0.1% is following, B:0.004% is following, Zr:0.02% is following, Ca:0.004% is following, Mg:0.002% is following and REM:0.002% with lower one or more.

In addition, as described later, both can on the basis that meets above-mentioned condition as the whole steel plate of mother metal and manufacture, weld, also can only process the position (becoming the position of welding heat affected zone) as the wish welding in the steel plate of mother metal, this position be welded meeting on the basis of above-mentioned condition.

And this welding process also can be applied in the time of the larger fillet weld seam of welding distortion.In addition, fillet weld seam carries out in lap joint, T joint, cross joint are first-class, and this welding process is for producing the T joint of king-sized welding distortion because of the relative position relationship of joint mother metal and the fillet weld seam of cruciform joint is effective especially.

The effect of invention

Adopt the present invention, can provide a kind of and can suppress with low cost and reliably also very good steel plate of welding distortion and erosion resistance.

Accompanying drawing explanation

Fig. 1 is the FEM calculation result that represents the impact of each material property value on Welding Angular Deformation amount.

Fig. 2 is the schematic diagram that represents the design conditions of FEM parsing.

Fig. 3 is the figure that represents to evaluate the test film that Welding Angular Deformation amount adopts.

Fig. 4 is the figure that represents the definition of Welding Angular Deformation amount.

Embodiment

In the present invention, limit the less chemical constitution of steel plate and the reasons are as follows of metallographic structure of welding distortion.

(A) chemical constitution of steel plate

The action effect of each composition of steel plate and the preferred amount of each composition are as described below.In addition, " % " relevant to amount refers to " quality % ".

C：0.02％～0.25％

C improves the most effective element to intensity, and is cheap element.But, in the time being less than 0.02%, need to be by use usually proof strength of other yuan simultaneously, result, can cause cost to rise.In addition, being greater than 0.25% ground containing sometimes, damage significantly weldability.Thereby the amount of C is 0.02%～0.25%.

Si：0.01％～0.7％

Si contributes to carry high-intensity element.But, in the time being less than 0.01%, cannot guarantee required intensity.In addition, be greater than 0.7% ground add time, can make significantly base metal tenacity and welding heat affected zone (HAZ) toughness deteriorated.Thereby the amount of Si is 0.01%～0.7%.

Mn：0.3％～2％

Mn is the element required in order to ensure intensity.But, in the time being less than 0.3%, cannot guarantee required intensity.In addition, be greater than 2% ground add time, weldability is deteriorated.Thereby the amount of Mn is 0.3%～2%.

below P:0.05%

P is present in the element in steel as impurity.In the time that the amount of P is greater than 0.05%, not only can segregate in crystal boundary and make toughness drop, and cause heat cracking in the time of welding, therefore, the amount that makes P is below 0.05%.

below S:0.008%

S is present in the element in steel as impurity.In the time that the amount of S is greater than 0.008%, encourage center segregation or a large amount of MnS that extends shape that generates, therefore, the mechanical properties of mother metal and HAZ is deteriorated.Thereby, make S amount on be limited to 0.008%.

cu: be less than 0.2%

Cu, usually used as the fundamental element that improves weathering resistance, adds in all beach climate-resistant steels, corrosion-resistant steel, but in the more dry environment of wafting under salinity at height, on the contrary reduces erosion resistance.In addition, if coexist with Sn, in the time of rolling, crack.Thereby, need to suppress the amount of Cu.Even contain as impurity, Cu amount also needs to be less than 0.2%.Preferably be less than 0.1%.

Cr：1％～2.5％

Cr improves the effective element of intensity to promoting hardening capacity.In order to obtain this effect, need to add more than 1%.But in the time being greater than 2.5%, toughness is deteriorated.Thereby the amount of Cr is 1%～2.5%.In addition, the preferred amount of Cr is 1%～1.8%.In addition, as described later, Cr makes the deteriorated element of erosion resistance under salt time-sharing environment, if but coexist with Sn, can suppress significantly its detrimentally affect.

below Mo:0.05%

Significantly increase because Mo can cause cost, therefore do not add.In addition, though there is the situation of sneaking into as impurity, even in this case, the amount of Mo is also below 0.05%.

Nb：0.005％～0.1％

Nb have make steel plate metallographic structure recrystallize the effect delaying.But, in the time that its amount is less than 0.005%, cannot obtain this effect.In addition, in the time being greater than 0.1%, the saturated and toughness of obvious damage HAZ of above-mentioned effect.Thereby the amount of Nb is 0.005%～0.1%.In addition, the preferred lower limit of the scope of Nb amount is 0.008%, and preferred upper limit is 0.020%.

Al：0.003％～0.1％

Al is for the necessary element of deoxidation.In order to carry out reliably deoxidation, need more than 0.003% amount.But in the time being greater than 0.1%, particularly in HAZ, toughness is easy to deteriorated.It is generally acknowledged that its reason is, be easy to form the alumina series inclusion particle of thick pencil.Thereby the amount of Al is 0.003%～0.1%.

below N:0.01%

N is present in the element in steel as impurity.In the time that the amount of N is greater than 0.01%, can cause base metal tenacity and HAZ toughness to worsen.Thereby, make N amount on be limited to 0.01%.

Sn：0.03％～0.50％

Sn becomes Sn ²⁺and dissolve, have the inhibitor utilizing in acidic chloride solution be used for suppress corrosion effect.In addition, by thering is the Fe of making ³⁺reduce rapidly, reduce the Fe as oxygenant ³⁺the effect of concentration, suppresses Fe ³⁺corrosion promoter action, therefore, promote high weathering resistance of wafting in salt time-sharing environment.In addition, there is the anode dissolution reaction that suppresses steel and the effect that promotes erosion resistance in Sn.And, by containing Sn, can bring into play the effect that also can promote the weathering resistance of Cr in the more environment of the salinity of wafting.These effect by contain Sn0.03% with on obtain, saturated in the time being greater than 0.50%.Thereby the preferred lower limit of the scope of Sn amount is 0.03%, preferred upper limit is 0.20%.

cu/Sn ratio: below 1

In the case of the steel that contains Sn, if coexist with Cu, erosion resistance significantly reduces.In addition, in the time manufacturing steel, also can cause rolling crack because containing Cu.Therefore, need to make Cu/Sn ratio, Cu amount is below 1 with the ratio of Sn amount.

Steel plate of the present invention has above-mentioned chemical constitution, and remainder is made up of Fe and impurity.At this, the meaning of impurity refers to the composition that a variety of causes due to manufacturing process is mainly sneaked into from such raw material such as ore, waste material in the time of industrial manufacture steel plate, is can not producing to the present invention the composition of allowing in dysgenic scope.

Steel plate of the present invention except above-mentioned element, the more than a kind composition that can contain as required at least 1 group selection from below the 1st group～the 3rd group as described below.Below, the composition that belongs to these groups is described.

the composition of the 1st group: Ti

below Ti:0.1%

Because Ti mainly plays the effect of deoxidant element, therefore, can contain as required.But, because also can utilizing Al, deoxidation carries out, therefore, might not contain.But, in the situation that Ti amount is more, be formed with Ti oxide compound or Ti-Al oxide compound, therefore, particularly can lose the ability of organizing miniaturization that makes little heat input welding heat affected zone.Ti amount in situation about therefore, containing is below 0.1%.In addition, contain in order stably to pass the deoxidation effect that Ti produces, it is more than 0.01% preferably making its amount.

the composition of the 2nd group: Ni, V, B, Zr

below Ni:3.5%

Because Ni improves base metal tenacity, and utilize hardening capacity to promote the element that also contributes to intensity to improve, therefore, can contain as required.But, because Ni is expensive element, therefore, while containing Ni, can cause cost significantly to rise excessive.In addition, if coexist with Sn, can make to exist the erosion resistance under muriatic environment deteriorated.Thereby, on the Ni amount in the situation that makes to contain, be limited to below 3.5%.Be preferably below 1.0%.More preferably below 0.5%.In addition, contain in order stably to pass the above-mentioned effect that Ni produces, it is more than 0.02% preferably making its amount.

below V:0.1%

Because V improves effective element to intensity, therefore, can contain as required.But in the time that the amount of V is greater than 0.1%, toughness is deteriorated largely, therefore, the V amount in situation about containing is below 0.1%.In addition, contain in order stably to pass the intensity raising effect that V produces, it is more than 0.005% preferably making its amount.

below B:0.004%

Propose high-intensity effect because B has the hardening capacity of lifting, therefore, can contain as required.But, in the time that the amount of B is greater than 0.004%, put forward high-intensity effect saturated, and the deteriorated tendency of toughness of mother metal, HAZ all becomes remarkable.Thereby the B amount in situation about containing is below 0.004%.In addition, contain raising hardening capacity that B produces and the effect of intensity in order stably to pass, preferably B amount is more than 0.0003%.

below Zr:0.02%

In steel, make the fine dispersion of nitride separate out because Zr has, put forward high-intensity effect, therefore, can contain as required.But, be greater than 0.02% ground add time, form thick precipitate, make toughness deteriorated, therefore, the Zr amount in situation about containing is below 0.02%.In addition, contain in order stably to pass the intensity raising effect that Zr produces, preferably Zr amount is more than 0.0003%.

the 3rd group: Ca, Mg, REM

below Ca:0.004%

Ca reacts with the S in steel, forms oxysulfide (oxysulfide) in molten steel.This oxysulfide is different from the inclusion that MnS etc. extends shape, can in rolling direction, not extend because of rolling processing, after rolling, be also spherical, therefore, there is the top etc. that suppresses the inclusion to extend shape as the welding crack of crackle starting point, the effect of hydrogen induced cracking, can contain as required.But, in the time that its amount is greater than 0.004%, likely cause toughness deteriorated.Thereby the Ca amount in situation about containing is below 0.004%.In addition, in order stably to obtain the effect that suppresses welding crack, hydrogen induced cracking, preferably Ca amount is more than 0.0003%.

below Mg:0.002%

Mg generates containing Mg oxide compound, becomes the generation core of TiN, has the effect that makes the fine dispersion of TiN, therefore, can contain as required.But in the time that its amount is greater than 0.002%, oxide compound too much causes ductility to reduce.Thereby, on the Mg amount in the situation that makes to contain, be limited to 0.002%.In addition, in order stably to obtain the effect that makes the fine dispersion of TiN, preferably Mg amount is more than 0.0003%.

below REM:0.002%

Because REM contributes to miniaturization, S fixing of welding heat affected zone tissue, therefore, can contain as required.But in the time that its amount is greater than 0.002%, REM becomes the toughness of mother metal is produced to dysgenic inclusion, therefore, the REM amount in situation about containing is below 0.002%.In addition, in order stably to obtain the miniaturization of tissue, the fixed effect of S, preferably R EM amount is more than 0.0003%.In addition, REM is that Y and Sc add that 15 elements of group of the lanthanides amount to the general name of 17 elements, can contain a kind of or two or more in these elements.In addition, the amount of REM refers to the total amount of these elements.

(B) metallographic structure

The ferrite of metallographic structure point rate is 10%～60%.From the viewpoint of preventing welding distortion, be good as the less mode of ferrite of the tissue that is easy to surrender, but in order to be suitable for the strength range of general strength steel, make the bound of ferrite point rate be respectively 60% and 10%.In addition, from the viewpoint of destroying toughness, the less mode of median size of ferritic structure is good.And, in the time that the median size of ferritic structure is greater than 30 μ m, cannot obtain sufficient destruction toughness, therefore, making its higher limit is 30 μ m.

Tissue except ferritic structure is bainite structure and/or martensitic stucture.Thereby point rate of bainite structure and/or martensitic stucture is 40%～90%.In addition, bainite structure and/or martensitic stucture refer to bainite structure, martensitic stucture or (bainite+martensite) tissue.

At this, ferrite is called to soft phase, and, bainite structure and/or martensitic stucture are called to hard phase.Because needs do one's utmost to prevent raw material surrender entirely at diversified temperature, therefore, preferably the hardness of hard phase is higher.On the other hand, by there being soft phase, as structure steel, yield strength and tensile strength can be adjusted to the scope that is suitable for standard etc.But, as mentioned above, can, by making in advance hard phase hardening suppress welding distortion, therefore, at this, carry out regulation welding distortion by the such index of hardness ratio of mutually hard and soft phase and suppress energy.According to contriver's etc. research, the hardness of hard phase be soft phase hardness more than 1.5 times time, can obviously improve welding distortion suppress can, therefore, hardness ratio is more than 1.5 times.

Then, to describing for the rolling, the heat treated condition etc. that obtain steel plate of the present invention.

Before hot rolling, first heating bloom, is Ac if make Heating temperature now ₃more than point, can be completed into austenite phase, under the state that there is no phase change portion not, homogenize, therefore, preferably making Heating temperature is Ac ₃more than point.Specifically, be preferably heated to 900 ℃～1200 ℃.And, be below 900 ℃ if make the final rolling temperature of thin-walled end in the time of hot rolling, crystal grain becomes appropriate size, and the destruction toughness of raw material is abundant, therefore, is preferably below 900 ℃.The lower limit of final rolling temperature is not particularly limited, as long as can make intensity be applicable to general strength range, can be just any condition.But, be more than 700 ℃ if make final rolling temperature, the anisotropy being produced by two-phase region processing is also not obvious, therefore comparatively desirable.Then rolling, also accelerates cooling grade better.Accelerating cooling in the situation that, preferably after rolling immediately or after some storage periods, the speed of cooling of central part is being controlled to 0.5 ℃/s～20 ℃/s.Cooling stop temperature preferably take 150 ℃～500 ℃ as target control.In addition, also can after rolling, suitably implement thermal treatment.Implementing, in heat treated situation, preferably to carry out anneal or temper, temperature is preferably selected respectively the temperature band of 800 ℃～1100 ℃, 300 ℃～700 ℃.

embodiment

Represent an example of steel plate of the present invention.Utilize each Heating temperature shown in table 2, precision work temperature, accelerate bloom cooling, that heat-treat condition is manufactured the moiety shown in table 1.The thickness of steel plate is 16mm.

table 1

table 2

In addition, table 3 represents respectively hardness ratio, Welding Angular Deformation amount, the thickness of slab reduction of yield-point YP, tensile strength TS, transition temperature vTrs, ferrite point rate, the ferrite median size of the steel plate obtaining like this, mutually hard and soft phase and peels off area occupation ratio.

table 3

In addition, in order to measure the tensile properties of the steel plate obtaining, gather test piece according to the test method described in JIS-Z-2201.Collection position is the thick near side (ns) of thickness of slab (t) direction (1/4) t and L direction (parallel with rolling direction).In addition, yield-point is obtained lower yield point as the trial speed of 10N/mms, is 0.2% endurance in the case of not occurring clear and definite yield-point.As the target value of tensile properties, yield-point YP is 350N/mm ²above, and tensile strength TS is 490N/mm ²～720N/mm ².

In addition, in order to measure the impact characteristics of the steel plate obtaining, gather test piece according to the test method described in JIS-Z-2202.Collection position is the thick near side (ns) of thickness of slab (t) direction (1/4) t and L direction (parallel with rolling direction), makes 2mmV notch (notch) Charpy test sheet, measures the percentage of brittle fracture surface under all temps, tries to achieve transition temperature.The target value of summer specific characteristic is that transition temperature is below 0 ℃.Structure observation utilizes opticmicroscope to carry out.To carrying out image analysis by observable image.For example, calculating particle diameter in the situation that, measure minor axis and major diameter, by itself and 1/2 try to achieve particle diameter.The particle diameter of observing each particle of trying to achieve to carrying out like this 100 visual fields is carried out to the value that arithmetical mean obtains and be defined as " median size ".In addition, the ferrite of metallographic structure point rate is tried to achieve for the area ratio of the area of 100 visual field observed quantities by calculating ferritic phase, and the area of these 100 visual field observed quantities utilizes observation similar to the above to draw.Bainite point rate and martensite divide rate too, but table 3 only represents ferrite point rate.

And, utilize following main points to evaluate the Welding Angular Deformation amount of fillet weld seam.

As shown in Figure 3, steel plate is made T-shaped welding test sheet (unit: mm), one-sided with the steel plate constraint that leg-of-mutton rigidity is higher, opposition side is implemented to the fillet weld seam of single pass.The welding material using is common 50 kilograms of flux-cored wires for steel (flux cored wire), and welding conditions is 10.4kJ/cm(200A-26V-30cm/min).After welding through after the sufficient time, test film is placed on and is determined on plate, at welding starting position, middle position, this 3 place of terminal location, utilize clearance measuring apparatus to measure the angular distortion amount θ defining in Fig. 4, using their mean value as Welding Angular Deformation amount.In addition, utilizing the Welding Angular Deformation amount of common general 50 kilograms of steel of the method mensuration to be approximately 1 ° of left and right, is 0.5 ° as the Welding Angular Deformation rank of target of the present invention.

And, about erosion resistance, utilizing SAE(Society of Automotive Engineers) J2334 tests the test film that the steel that certainly obtain are obtained and evaluates.SAE J2334 test is by moistening: 50 ℃, 100%RH, 6 hours, salinity adhere to: 0.5%NaCl, 0.1%CaCl ₂, 0.075%NaHCO3 aqueous solution dipping, 0.25 hour, dry: 60 ℃, 50%RH, 17.75 hours are as 1 circulation accelerated test of (adding up to 24 hours), etch state and weather exposure test similar (Nagano win under husband, mountain just people, interior Tian Renzhu: Viewpoint of Eco materials, be total to and stand publication (2004), p.74).In addition, this test is to simulate the test that the salt amount of wafting is greater than the harsh like this corrosive environment of 1mdd.

After 120 loop ends of SAE J2334 test, remove the rusty scale on each test film surface, measure thickness of slab reduction.At this, " thickness of slab reduction " is the average thickness of slab reduction of test film, is that the weight minimizing of use-testing front and back and the surface-area of test film calculate.

In addition, in order to investigate the separability of resistance to application, utilize air-jet method to the mode application modified epoxy coating (BANNOH200: Chinese coating system) take dry film thickness as 150 μ m on the test film of 150mm × 70mm size, draw lattice (cross cut) afterwards to reach the degree of depth of steel substrate, similarly utilize SAE J2334 test to evaluate.

As a result, in the steel plate (comparative example) of mark 1-e, precision work temperature is higher is 910 ℃, and to make cooling conditions be air cooling, and therefore, ferritic growing amount is more, and, the ferrite grain growth of generation and median size becomes large.Therefore, tensile strength diminishes.In addition, no matter firmly with the hardness ratio of soft phase whether in scope of the present invention, it is large that Welding Angular Deformation amount all becomes.It is generally acknowledged that its reason is, be broken as ferrite and the balance of the amount of hard phase of soft phase.As mentioned above, the tensile strength of the steel plate of mark 1-e is lower, and Welding Angular Deformation amount is also larger, is therefore the steel that are not suitable as structure steel plate.

Then, in the steel plate (comparative example) of mark 1-f, making the speed of cooling after heating is 25 ℃/sec, therefore, overquenching and do not generate ferrite, it is large that the tensile strength of steel plate self becomes, and toughness also reduces largely.Although Welding Angular Deformation amount is less, be also the steel that are not suitable as structure steel plate.

In addition, in the steel plate (comparative example) of mark 12-b, making water-cooled stop temperature is 120 ℃, is quenched to lower temperature, therefore, firmly diminishes with the hardness ratio of soft phase, and Welding Angular Deformation quantitative change is large.

And, in the steel plate (comparative example) of mark 40-46, discontented foot steel composition given to this invention, the toughness drop of steel plate self.The steel that are not suitable as structure steel plate.In the steel plate (comparative example) of mark 47, in the time of rolling, produce crackle, therefore, will test termination.In addition, in the steel plate (comparative example) of mark 48, the Sn amount in steel composition given to this invention does not meet, and erosion resistance reduces.

With respect to this, in the steel plate of the known inventive example being represented by other mark, tensile properties is all that yield-point YP is 350N/mm ²above, and tensile strength TS is 490N/mm ²～720N/mm ²the Primary Steel of level, transition temperature vTrs, ferrite divide rate, ferrite median size, mutually hard and soft phase hardness ratio also in proper range, and Welding Angular Deformation amount also enters in 0.5 ° of target, therefore, is suitable as structure steel plate.Also known, also there is higher erosion resistance, although corrosion has appearred in the lattice portion of the drawing in the situation that of application, because peeling off of steel plate is all less, therefore, the interval of studying for a second time courses one has flunked of application can be elongated.

utilizability in industry

As described above, adopt the present invention, can provide a kind of can and suppress the steel plate of welding distortion, excellent corrosion resistance reliably with low cost in fillet weld seam.

Claims

1. the less and excellent corrosion resistance of welding distortion, thickness are a steel plate more than 15mm, it is characterized in that,

There is such chemical constitution, , in quality %, contain C:0.02%～0.25%, Si:0.01%～0.7%, Mn:0.3%～2%, below P:0.05%, below S:0.008%, Cu: be less than 0.2%, Cr:1%～2.5%, below Mo:0.05%, Nb:0.005%～0.1%, Al:0.003%～0.1%, following and Sn:0.03%～0.50% of N:0.01%, remainder is made up of Fe and impurity, and Cu/Sn ratio is below 1, metallographic structure is made up of 10%～60% ferritic structure and 40%～90% bainite structure and/or martensitic stucture, and, the median size of this ferritic structure is below 30 μ m, the hardness of bainite structure and/or martensitic stucture is more than 1.5 with the ratio of the hardness of ferritic structure.

2. the less and excellent corrosion resistance of welding distortion according to claim 1, thickness are steel plate more than 15mm, it is characterized in that,

In quality %, this steel plate also contains below Ti:0.1%.

3. the less and excellent corrosion resistance of welding distortion according to claim 1 and 2, thickness are steel plate more than 15mm, it is characterized in that,

In quality %, this steel plate also contain that Ni:3.5% is following, V:0.1% following, B:0.004% is following and Zr:0.02% with lower one or more.

4. the less and excellent corrosion resistance of welding distortion according to claim 1 and 2, thickness are steel plate more than 15mm, it is characterized in that,

In quality %, this steel plate also contain that Ca:0.004% is following, Mg:0.002% following and REM:0.002% with lower a kind of or two or more.

5. the less and excellent corrosion resistance of welding distortion according to claim 3, thickness are steel plate more than 15mm, it is characterized in that,